Carbon-coated TiO2 Research Articles

Nitrogen Doping and Carbon Coating Affects Substrate Selectivity of TiO2 Photocatalytic Organic Pollutant Degradation.

A series of carbon-coated, nitrogen-doped titanium dioxide photocatalysts was produced and characterized. N-doped TiO2 powder samples were prepared using a sol-gel method and subsequently used for making doped-TiO2 thin films on glass substrates. Carbon layers were coated on the films by a thermal decomposition method using catechol. Diffuse reflectance spectra and Mott-Schottky analyses of the samples proved that nitrogen doping and carbon coating can slightly lower the band gap of TiO2 , broaden its absorption to visible light and enhance its n-type character. According to photocatalytic tests against model contaminants, carbon-coated nitrogen-doped TiO2 films have better performance than simple TiO2 on the degradation of Rhodamine B dye molecules, but are poorly effective for degrading 4-chlorophenol molecules. Several possible explanations are proposed for this result, supported by scavenging experiments. This reveals the importance of a broad substrate scope when assessing new photocatalytic materials for water treatment, something which is often overlooked in many literature studies.

Carbon-coated porous TiO2 layers templated by core-shell polymer particles: Film processing and charge transfer resistance assessment

The performances of titanium dioxide (TiO2) thin films used in photoelectrochemical applications (solar cells, water splitting, photocatalysis, etc) highly depend on their morphology and interface. In this work, we describe a straightforward strategy for designing conductive carbon-coated TiO2 porous layers allowing for the tuning of interfacial charge transfers. Increased specific surface and improved conductivity are expected from the porosity and the carbon coating, respectively. In practice, polystyrene/polyacrylonitrile (PS-PAN) and polystyrene/polydopamine (PS-PDA) core-shell particles synthesized by emulsion polymerization are considered as templating agents for the production of carbon-coated and ordered porous TiO2 layers. After spin coating deposition of the particles, infiltration of the TiO2 precursor and calcination, voids are created in the film by thermal degradation of the PS cores whereas PAN and PDA produced carbon at the surface of the TiO2 inverse opal matrix. Uncoated PS particles are also considered as benchmark templating agents. Size and composition of the polymer particles as well as the morphology and electronic properties of the corresponding porous TiO2 films are evaluated. In particular, the charge transfer resistance of the films is investigated via Electrochemical Impedance Spectroscopy (EIS) as a preliminary assessment of these unprecedented carbon-coated porous TiO2 layers as semiconducting materials.

Sodium Induced Morphological Changes of Carbon Coated TiO2 Anatase Nanoparticles - High-Performance Materials for Na-Ion Batteries

The most promising candidate as an everyday alternative to lithium-ion batteries (LIBs) are sodium-ion batteries (NIBs). This is not only due to Na abundance, but also because the main principles and cell structure are very similar to LIBs. Due to these benefits, NIBs are expected to be used in applications related to large-scale energy storage systems and other applications not requiring top-performance in terms of volumetric capacity. One important issue that has hindered the large scale application of NIBs is the anode material. Graphite and silicon, which have been widely applied as anodes in NIBs, do not show great performance. Hard carbons look very promising in terms of their abundance and low cost, but they tend to suffer from instability, in particular over the long term. In this work we explore a carbon-coated TiO2 nanoparticle system that looks very promising in terms of stability, abundance, low-cost, and most importantly that safety of the cell, since it does not suffer from potential sodium plating during cycling. Maintaining a nano-size and consistent morphology of the active material is a crucial parameter for maintaining a well-functioning cell upon cycling. In this work we applied Anomalous Small Angle X-Ray Scattering (ASAXS) for the first time at the Ti K-edge of TiO2 anatase nanoparticles on different cycled composite electrodes in order to have a complete morphological overview of the modifications induced by sodiation and desodiation. This work also demonstrates for the first time that the nanosize of the TiO2 is maintained upon cycling, which is in agreement with the electrochemical stability.

Probing the facet-dependent intermediate in the visible-light degradation of RhB by carbon-coated anatase TiO2 nanoparticles

The Facet-dependent photocatalytic process related to the degradation of organic pollutants by semiconductor catalysts is of great significance for understanding the photocatalytic mechanism of nanomaterials and improving their catalytic performance. Herein, the titanium dioxide catalysts with {001} or {101} dominant exposed facets coated with carbon (TiO2(001)/C and TiO2(101)/C) were synthesized by a hydrothermal method, and the photo-degradation research of rhodamine B (RhB) was analyzed by using UV–visible absorption spectroscopy, fluorescence spectroscopy and time-resolved fluorescence spectroscopy. The results demonstrated that the degradation of RhB was the competition for both N-deethylation and the destruction of aromatic ring reactions. The N-deethylation of RhB molecules dominated the reaction in the TiO2(001)/C system during the initial irradiation period. Whereas, both N-deethylation and cleavage of the aromatic ring occurred simultaneously in TiO2(101)/C/RhB system. The results of the fluorescence spectra and fluorescence lifetime analysis also suggested that the degradation rate of the intermediate product (Rh-110) is faster for TiO2(001)/C than TiO2(101)/C. We proposed a possible explanation that the carbonaceous species on the surface of TiO2 can absorb visible light to assist the degradation of RhB. The difference in surface properties and energy band structures lead to the different degradation processes and facet dependent features. Our findings presented the intermediate evidences for revealing the relation between the photocatalytic activity and exposed facets of TiO2 nanoparticles.

All-solid-state Z-scheme photocatalysts of g-C3N4/Pt/macroporous-(TiO2@carbon) for selective boosting visible-light-driven conversion of CO2 to CH4

The artificial photosynthesis for visible-light-driven CO2 reduction with H2O is promising to solve both energy and environmental issues simultaneously. Herein, we have successfully fabricated all-solid-state Z-scheme ternary photocatalysts, consisting of two isolated photochemical systems of graphitic carbon nitride (g-C3N4) and three-dimensional ordered macroporous carbon-coated TiO2 (3DOM-TiO2@C) combined with Pt nanoparticles as electron-transfer system. Photonic crystal structure and carbon-coated nanolayers of 3DOM-TiO2@C support enhance visible light-harvesting efficiency. The vectorial photoelectron transferring of TiO2@C → Pt → g-C3N4 boosts the separation and surface enrichment efficiencies of photogenerated electrons and holes. All-solid-state Z-scheme ternary photocatalyst exhibits the outstanding yields of CH4 (6.56 μmol h−1, 0.1 g catalyst) and high-efficient quantum efficiency (5.67%) during visible-light-driven conversion of CO2 with H2O. The surface enrichment of electrons and CO2 is the rate-determining step of selective CO2 photoreduction. This study is expected to throw new light on the fabrication of high-efficient photocatalyst for CO2 conversion to hydrocarbon.

Single yttrium sites on carbon-coated TiO2 for efficient electrocatalytic N2 reduction.

We report single yttrium sites anchored on carbon-coated TiO2 for efficient and stable electrocatalytic N2 fixation, delivering an NH3 faradaic efficiency exceeding 11.0% and an NH3 yield rate as high as 6.3 μgNH3 h-1 mgcat.-1 at low overpotentials, thus surpassing many reported metal electrocatalysts.

Structural Study of Carbon-Coated TiO2 Anatase Nanoparticles as High-Performance Anode Materials for Na-Ion Batteries

In this work, we study the electronic and atomic structural modifications occurring in TiO2 anatase nanoparticles as anode materials in Na-ion batteries upon sodiation and desodiation. The structur...

Carbon-coated, hierarchically mesoporous TiO2 microparticles as an anode material for lithium and sodium ion batteries

Hierarchically porous anatase TiO2 microparticles are synthesized in supercritical methanol (scMeOH) in the presence of organic surface modifiers such as oleylamine, oleic acid, and poly(ethylene glycol)methyl ether/citric acid (PEGME/CA) mixture. Primary TiO2 nanoparticles (5–9 nm) that loosely aggregate to form secondary micron-sized particles (0.2–1.5 μm) are obtained in the presence of PEGME/CA. The surface modifier aids the effective suppression of undesirable crystal growth because their molecules cap the surfaces of growing particles in scMeOH. An ultrathin, conformal and uniform carbon layer with 1–2 nm thickness is then formed on the surface of the TiO2 particles by heat treatment. The carbon-coated TiO2 particles delivers 231 mAh g−1 at 0.1 C after 50 cycles and 85 mAh g−1 at 10 C in a lithium-ion battery cell, 275 mAh g−1 at 0.1 C after 50 cycles, 40 mAh g−1 at 10 C, and high capacity retention of 94% after 450 cycles in a sodium-ion battery cell. The excellent electrochemical performance of the TiO2 particles is attributed to the small crystallite size, continuous electronic network formed by the close contact of individual carbon-coated primary TiO2 particles, and the effective penetration of the mesopores by the electrolytes.

Synthesis of Carbon-Coated TiO2 by Underwater Discharge With Capillary Carbon Electrode

This paper is focused on carbon coating of anatase type TiO2 by underwater discharge with a capillary in water carbon electrode. The discharge electrode consists of a graphite electrode covered by an alumina tube for insulation and a ground electrode. The aqueous solution used for discharging is tap water with an electric conductivity of about $120~\mu \text{S}$ /cm. The applied power for TiO2 carbon coating is about 500 W. As a result of TEM and energy dispersive spectrum measurements, a carbon layer with thickness of several nanometers was measured on the surface of TiO2. Raman analysis also confirmed that the layer is either graphite or glassy carbon.

Lysine-modified TiO2 nanotube array for optimizing bioelectricity generation in microbial fuel cells

As the carrier of electroactive bacteria and part of the electron migration path, the anode is a restricting factor for the power density of microbial fuel cells (MFCs). In this study, carbon-coated TiO2 nanotube array (TNT/HL) was synthesized by anodization and thermal treatment, for use as anodes in MFCs to promote power production. Due to the sucker structure and the carbon attachment, the TNT/HL anode increased the bacterial loading capacity when exposed under lamplight or natural light. Single-chamber MFCs with the TNT/HL anode achieved a maximum power density of 0.88 W/m2, which is much higher than that of MFCs using the common commercial carbon cloth (CC) anode (0.61 W/m2). Further investigation attributed such superior results to the better biocompatibility, enlarged electroactive surface, decreased electric resistance and Tafel slope of the as-prepared TNT/HL anode. This study introduces a promising anode material for MFCs with high conductivity, high current density, and fast extracellular electron transfer (EET).

Clean Block Copolymer Microparticles from Supercritical CO2: Universal Templates for the Facile and Scalable Fabrication of Hierarchical Mesostructured Metal Oxides.

Metal oxide microparticles with well-defined internal mesostructures are promising materials for a variety of different applications, but practical routes to such materials that allow the constituent structural length scales to be precisely tuned have thus far been difficult to realize. Herein, we describe a novel platform methodology that utilizes self-assembled block copolymer (BCP) microparticles synthesized by dispersion polymerization in supercritical CO2 (scCO2) as universal structure directing agents for both hydrolytic and nonhydrolytic sol-gel routes to metal oxides. Spherically structured poly(methyl methacrylate- block-4-vinylpyridine) (PMMA- b-P4VP) BCP microparticles are translated into a series of the corresponding organic/inorganic composites and pure inorganic derivatives with a high degree of fidelity for the metal oxides TiO2 and LiFePO4. The final products are comprised of particles close to 1 μm in size with a highly ordered internal morphology of interconnected spheres between 20-40 nm in size. Furthermore, our approach is readily scalable, enabling grams of pure or carbon-coated TiO2 and LiFePO4, respectively, to be fabricated in a facile two step route involving ambient temperature mixing and drying stages. Given that both length scales within these BCP microparticles can be controlled independently by minor variations in the reagent quantities used, the present general strategy could represent a milestone in the design and synthesis of hierarchical metal oxides with completely tunable dimensions.

Hydrothermal Carbon-Coated TiO2 as Support for Co-Based Catalyst in Fischer–Tropsch Synthesis

A range of cobalt catalysts, prepared using TiO2 enwrapped with a hydrothermal carbon (HTC) layer, was used as a support for the Fischer–Tropsch synthesis (FTS). The effects of the HTC coating thickness and annealing process of HTC–TiO2 on the structure and performance of the cobalt catalysts were investigated. The HTC coating with enrichment functional groups (e.g., COOH and COH) generated a strong interaction with the Co species during catalyst preparation and finally enhanced cobalt oxide dispersion. Furthermore, the protection of the surface of TiO2 by a HTC coating improved the reducibility of the cobalt catalysts. The Co particle size was correlated with the thickness of HTC coating and the HTC–TiO2 support annealing process. It was found that the HTC–TiO2 support with a coating thickness of 8 nm and without an annealing process gave catalysts with a cobalt particle size of 8.6 nm and optimal FTS performance. The corresponding Co/8C-TiO2 catalyst exhibited an activity 2.4 times higher than that of a...

Synthesis of Nanocrystalline Oxide Ceramic Materials:a Carbon Nanoreactor Concept

Carbon-coated nanocrystalline oxides TiO2@C, Al2O3@C and calcium aluminate C12A7@C were synthesized, and the effect of carbon coating on their thermal stability and reactivity was studied. It was found that the carbon coating prevents sintering of the titanium nanoparticles and contributes to stabilization of their size. Thus, the particle size of anatase can be stabilized at level of 10-12 nm even after heat treatment at 750°C. Deposition of the carbon coating on γ-Al2O3 prevents growth of the alumina nanoparticles and substantially improves their thermal stability. Complete Al2O3 conversion to corundum occurs after heat treatment at 1250°C, whereas practically no corundum is formed under similar conditions for Al2O3@C. Dispersed calcium aluminate C12A7 particles resistant to sintering at high-temperature were synthesized inside the carbon shell. Meanwhile, intense sintering at high temperatures was observed for the samples without the carbon coating. The carbon shell prevents sintering and makes it possible to synthesize samples in a disperse state even at 1450°C. According to TEM data, characteristic sizes of C12A7 particles inside the carbon coating range from 100 nm to several microns. So, the core-shell approach can be used to stabilize the size of the oxide core nanoparticles up to temperatures when their reaction with the coating material occurs. In the case of the carbon shell, this is the temperature when the carbothermal reduction of the oxide core takes place.

Highly ordered three-dimensional TiO2@C nanotube arrays as freestanding electrode for sodium-ion battery

Highly ordered three-dimensional carbon-coated TiO2 nanotube arrays (TiO2@C NTAs) directly grown on Ti current collector have been fabricated using a combination of anodization and hydrothermal method. The grown TiO2@C NTAs were vertically aligned on the Ti foil with a diameter of around 100nm and length of 10μm. Benefiting from their structure features, the as-fabricated TiO2@C NTAs anode exhibits excellent sodium storage in terms of high reversible capacity (232mAhg−1 over 500 cycles at current density of 200mAg−1) and superior rate capability (68mAhg−1 at current density of 6.4Ag−1).

Excellent sodium storage performance of carbon-coated TiO2: Assisted with electrostatic interaction of surfactants

To enhance the electronic conductivity of TiO2, carbon-coating has been used as a simple and effective method for improving the electrochemical performances of TiO2 in sodium ion batteries. In this work, considering the internal connection between TiO2 and the coated carbon-layer, we synthesized carbon-coated TiO2 composites (TiO2/C) via hydrothermal method and subsequent calcination, assisted with different types of surfactant as carbon sources. Due to strong electrostatic attraction, cationic surfactant CTAB (cetyltrimethyl ammonium bromide) generates a uniformly-coated carbon layer onto TiO2 surface, which enables good electronic conductivity and fast kinetics of the product. Therefore, TiO2/C assisted with CTAB as carbon source (TiO2/C-C) shows optimal sodium storage performance with excellent specific capacity (303 mA h g−1 at 0.1 C) and satisfying cycling stability, offering promising anode for constructing high capacity sodium ion batteries.

Biotemplating Synthesis of Graphitic Carbon-Coated TiO2 and Its Application as Efficient Visible-Light-Driven Photocatalyst for Cr6+ Remove

TiO2 and graphitic carbon (GC) composites with hierarchical pore structures were synthesized using Staphylococcus aureus (ATCC6538) as the biotemplate to modify Degussa P25 TiO2 powder. Then, the composites were applied as photocatalysts for Cr6+ reduction under visible light irradiation. X-ray diffraction, Raman spectroscopy, transmission electron microscopy, nitrogen adsorption–desorption analysis, and X-ray photoelectron spectroscopy demonstrated the presence of a GC coating layer and a unique anatase/rutile mixed crystal phase of TiO2 even after heating at 800 °C. The novel TiO2@GC composites, especially the S-P25-800 sample, which possessed abundant hierarchical mesoporous structures, exhibited strong catalytic activities in Cr6+ photoreduction under visible light. This work provides light to overcome the challenge on synthesis of GC modified TiO2 photocatalysts with the highly reactive but heat-labile anatase main crystal phase at high temperature. Furthermore, the present results demonstrated that ...

Composite hollow nanostructures composed of carbon-coated Ti3+self-doped TiO2-reduced graphene oxide as an efficient electrocatalyst for oxygen reduction

Cost-effective durable and highly active electrode materials have become greatly desirable in the electrocatalytic oxygen reduction reaction (ORR), a crucial element in energy devices. In particular, the low intrinsic conductivity and poor reactivity of TiO2 are believed to hinder the efficient applicability of this material as an ORR catalyst. Herein, we report for the first time an efficient one-step approach to synthesize conductive Ti3+ self-doped carbon-coated TiO2 anchored on reduced graphene oxide (rGO) hollow nanospheres. A remarkable 11-fold improvement of the conductivity of TiO2 with an optimized rGO(10%)/TiO2 sample is herein reported. The rGO/TiO2 hollow nanospheres unveiled comparable activity to a conventional Pt/C reference. Most importantly, improved stability and remarkable methanol tolerance were achieved. The results were attributed to a cooperative effect of the hybridization of TiO2 with rGO, Ti3+ self-doping and the formation of a carbon-coating layer over the TiO2 particles. The selected design for the morphology of this novel electrocatalyst was further confirmed to play a crucial role in providing an enhanced number of active sites for oxygen reduction. This new nanocomposite is believed to exhibit promising applicability in a wide range of research areas including energy storage and conversion, photocatalysis, and gas sensors.

Self-Assembled Synthesis of Mesocrystalline TiO2@C-rGO Hybrid Nanostructures for Highly Reversible Sodium Storage

With the aim of enhancing the electrochemical kinetics and capacity of the TiO2 electrode for Na ion batteries (NIBs), we have designed a hybrid material of carbon-coated TiO2 mesocrystals anchored on reduced graphene oxide (TiO2@C-rGO). Such hybrid nanostructures are fabricated through a facile one-step route including in situ growth of oriented self-assembly of TiO2 mesocrystals on GO. TiO2@C-rGO possesses a very large surface area (279 m2 g–1), mesoporous nature, and single-crystal-like structure. It is also found that the capacity of TiO2 electrode for NIBs could be improved by carbon coating at a low current rate, but pure TiO2 shows better rate performance than that of TiO2@C. Remarkably, the enhanced electrochemical kinetics and large capacity can be simultaneously achieved by designing hybrid material. The hybrid nanostructures exhibit a highly reversible capacity of 300 mAh g–1 at 100 mA g–1, superior rate capability, and long-term cycling stability (a stable capacity of 159 mAh g–1 can be mainta...

Sodium Insertion/Extraction in Carbon-Coated Nanoscale Anatase TiO2

Rechargeable sodium batteries, as the replacement of rechargeable lithium batteries, are attracting much attention for large-scale applications such as electric vehicles and stationary energy storage due to the abundant resource of sodium compared to lithium. Up to now, there are only a few materials which have reasonable performances as negative electrodes of rechargeable sodium batteries, such as alloy materials [1], hard carbon [2], and sodium titanium oxides [3]. Recently, TiO2, an attractive alternative negative electrode material to graphite for rechargeable lithium batteries, was also investigated for rechargeable sodium batteries [4, 5]. However, the reported reversible capacities of TiO2 electrodes are less than 200 mAh g-1 and the Na insertion/extraction mechanism is still unclear. In the previous study, carbon-coated anatase TiO2 (TiO2/C) nanopowders were investigated as negative electrode material for rechargeable sodium battery with Na[FSA]-[C3C1pyrrr][FSA] (FSA = bis(fluorosulfonyl)amide; C3C1pyrr = N-methyl-N-propylpyrrolidinium) ionic liquid electrolyte [6]. In the present study, the electrochemical performance of TiO2/C electrode was further investigated in Na[FSA]-[C3C1pyrrr][FSA] ionic liquid electrolyte, and the Na insertion/extraction mechanism was explored. The TiO2/C electrode shows a high reversible discharge capacity of 275 mAh g-1 at 10 mA g-1 at 363 K. The observed capacity is higher than that reported for anatase TiO2 nanorods (193 mAh g-1 at 10 mA g-1) in organic electrolytes at room temperature [5]. Moreover, this capacity is comparable to that of a hard carbon negative electrode (260 mAh g-1) in Na[FSA]-[C3C1pyrrr][FSA] electrolyte [7]. Since the density of anatase TiO2 (ca. 3.9 g cm-3) is much higher than that of hard carbon (ca. 1.52 g cm-3), the TiO2/C nanopowder electrode is a promising negative electrode material for the rechargeable sodium batteries with high volumetric energy densities. The Na insertion/extraction mechanism was investigated by means of ex-situ X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive X-ray (EDX) spectroscopy and electron diffraction. Ex-situ XRD analysis of the TiO2/C electrodes in the different charged/discharged states show that during the charge process, the anatase TiO2 crystal phase disappears and a new crystal phase is formed. During the discharge process, the newly formed crystal phase disappears and no anatase TiO2 phase appears again. According to the TEM, EDX and electron diffraction studies, the fully discharged TiO2/C electrode is suggested to consist of amorphous TiO2, amorphous Na2TiO3 and cubic TiO phases, and the crystal phase in the fully charged TiO2/C electrode is possibly a solid solution of cubic Na2TiO3 and cubic TiO phases. Thus, amorphous TiO2, amorphous Na2TiO3 and cubic TiO are regarded as active electrode materials, and reversibly react with Na ions to form Na2TiO3•TiO solid solution. The TiO2/C negative electrode also exhibits a high rate capability and good cycling performance. When the charge-discharge rate is increased, the shapes of the charge-discharge curves remain unchanged. The discharge capacities decrease gradually with an increase in the current rate. The TiO2/C electrode shows reversible discharge capacities of 174 and 93 mAh g-1 at current rates of 500 and 2000 mA g-1, respectively, corresponding to about 69 and 37% of the capacity at 20 mA g -1. The discharge capacity is 174 mAh g-1 after 400 cycles at a current rate of 200 mA g-1, exhibiting only 10% drop in capacity. After 1000 cycles, the capacity decreases by approximately 21%. Acknowledgements This study was partly supported by the Advanced Low Carbon Technology Research and Development Program (ALCA, No. 3428) of the Japan Science and Technology Agency (JST) and the “Elements Strategy Initiative to Form Core Research Center" program of the Japanese Ministry of Education, Culture, Sports, Science and Technology (MEXT).

Size-Tunable Olive-Like Anatase TiO2 Coated with Carbon as Superior Anode for Sodium-Ion Batteries.

Olive-shaped anatase TiO2 with tunable sizes in nanoscale are designed employing polyvinyl alcohol (PVA) as structure directing agents to exert dramatic impacts on structure shaping and size manipulation. Notably, the introduced PVA simultaneously serves as carbon sources, bringing about a homogenous carbon layer with intimate coupling interfaces for boosted electronic conductivity. Constructed from tiny crystalline grains, the uniformly dispersed carbon-coated TiO2 nano-olives (TOC) possess subtle loose structure internally for prompt Na+ transportations. When utilized for sodium-ion storage, the size effects are increasingly significant at high charge-discharge rates, leading to the much superior rate performances of TOC with the smallest size. Bestowed by the improved Na+ adsorption and diffusion kinetics together with the promoted electron transfer, it delivers a high specific capacity of 267 mAh g-1 at 0.1 C (33.6 mA g-1 ) and sustains 110 mAh g-1 at a rather high rate of 20 C. Even after cycled at 10 C over 1000 cycles, a considerable capacity of 125 mAh g-1 with a retention of 94.6% is still obtained, highlighting its marvelous long-term cyclability and high-rate capabilities.